A flat panel display (FPD) that utilizes an optical film (e.g., polarizer and retardation film) can achieve high-resolution display, and has been widely used as a display device (e.g., TV).
Examples of the retardation film include a quarter-wave plate that converts linearly polarized light into circularly polarized light, and a half-wave plate that converts the plane of vibration of linearly polarized light by 90°. Such a retardation film can achieve accurate conversion of specific monochromatic light so that ¼λ or ½λ retardation occurs.
However, a known retardation film has a problem in that polarized light that passes through the retardation film is converted into colored polarized light. Specifically, since a material that forms the retardation film has wavelength dispersion with regard to retardation, and a polarization state distribution corresponding to each wavelength occurs for white light that includes different light beams in the visible region, it is impossible to achieve accurate ¼λ or ½λ retardation over the entire wavelength band.
In order to solve the above problems, various wideband retardation films that can achieve uniform retardation for light over a wide wavelength band (i.e., retardation films having reverse wavelength dispersion) have been studied (see Patent Documents 1 to 6, for example).
It has been desired to reduce the thickness of the flat panel display as much as possible along with an improvement in performance and widespread use of mobile information terminals (e.g., mobile personal computer and mobile phone) and the like. Therefore, a reduction in thickness of the retardation film has also been desired.
It has been considered that it is most effective to produce a retardation film by applying a polymerizable composition which includes a low-molecular-weight polymerizable compound to a film base in order to reduce the thickness of the retardation film. Various low-molecular-weight polymerizable compounds having excellent wavelength dispersion, and various polymerizable compositions using such polymerizable compounds have been proposed (see Patent Documents 7 to 23, for example).
However, the low-molecular-weight polymerizable compounds or the polymerizable compositions disclosed in Patent Documents 7 to 23 and the like have a number of problems in that reverse wavelength dispersion may be insufficient, or it may be difficult to apply the low-molecular-weight polymerizable compounds or the polymerizable compositions to a film due to a high melting point that is not suitable for an industrial process, or the temperature range in which liquid crystallinity is obtained may be very narrow, or solubility in a solvent generally used for an industrial process may be low. Moreover, since the above low-molecular-weight polymerizable compounds and the like are synthesized by a plurality of steps using a synthesis method that utilizes an expensive reagent, the production cost increases.